Rear Crossmember.

[FluxMorz]

Okay here is the update now that I have picked up the car and driven it home. I'll try and explain it as best as I can. It may end up being edited in the event I get something wrong.

Firstly, further example that I know nothing about cars: The car wasn't even lowered. My father had questioned this a couple times in the past. Seeing it hoisted up proved him correct. The camber on the tyres is stock standard. The wheels are 18 inch btw. The suspension specialist said he had worked on this kind of incident multiple times before, though admittedly hadn't worked on BMW sub frame in a long while.

The problem is that the rear sub frame area is all very exposed to hitting objects sticking out of the road (large rocks embedded in dirt roads, etc) and if the front of the cross member takes a hard hit to its forward side under there, then with the force of the moving car, it is possible to bend the cross member forward - pushing the trailing arms and gearbox fractionally and redirecting the tow of each tyre inwards.

This causes the tyres to compete with each other which wears the tyres excessively and causes the car to move around on the road a LOT with new tyres (which mine does). This appears to be what has occurred in my case. The damage is not visible on the cross member itself (it is bent so the angle is slightly deviated), and there is no visible damage (that we noted) to the rest of the sub frame. What makes the damage clearer is the toe of the tyres.

I edited the above oem graphic to hopefully explain what I mean a little more. I hope it helps.

 

[TaffZee]

Oooh Its Fluxed then. Only answer is a replacement, wouldnt give up on it though someone will have an answer....Good Luck.

 

[Cooper]

Here is a great document that tells you everything you need to know about suspension components. We have the E36/7 so look out for that. I downloaded a copy for my personal use so if the link is not allowed I can email it to anyone.

http://www.bmwmotorsports.org/BMW_docs/x5align.pdf

 

[oldcarman]

I hope someone with a better understanding than I comes along as I'm really not getting this at all. What kind of hit would have only done damage to these parts and caused problems with both tires equally? JIM

 

[Cooper]

I hope someone with a better understanding than I comes along as I'm really not getting this at all. What kind of hit would have only done damage to these parts and caused problems with both tires equally? JIM

Hi Jim, I hope so too. I have been doing some research and bent this and that is mentioned but never HOW the damage occurred, except for hitting things as Flux mentioned. Perhaps pot holes and bumps/dips in the road contribute to metal fatigue and such. Here in Hobart there are many tree roots going under the roads in many areas and if you hit those at speed I cannot see how you would NOT do any damage! . In flux's case it seems that the gear box [auto] has also been slightly moved out of spec somehow.

 

[t-tony]

I'm wondering if he's confusing gearbox and Diff. I can't see how you could damage the gearbox enough to bend/twist the rear x-member without causing major damage to the gearbox in my opinion based on being in this trade for 40+ years.

 

[oldcarman]

Hi Jim, I hope so too. I have been doing some research and bent this and that is mentioned but never HOW the damage occurred, except for hitting things as Flux mentioned. Perhaps pot holes and bumps/dips in the road contribute to metal fatigue and such. Here in Hobart there are many tree roots going under the roads in many areas and if you hit those at speed I cannot see how you would NOT do any damage! . In flux's case it seems that the gear box [auto] has also been slightly moved out of spec somehow.

Hi Cooper, thanks for the transmission info. It falls in line with there having to be other areas of damage showing up somewhere but doesn't really get us any closer to a solution. What are the odds that one could whack that rear diff hard enough and in such an exact spot as to change the camber equally on both sides. I have never, except in extreme accident seen a rear housing bent. Axels break, wheels bend, etc but a housing never. There are just too many weaker pieces that would give up first. IMHO. Has Flux been doing any bus jumping or other stunts when delivering those pizzas? JIM

 

[zedonist]

So the garage has seen this numerous times before where a big rock sticking out the road has been hit by a car bending the sub frame but leaving no damage.

This sounds suspect to me, and would take with a pinch of salt.

That said if the toe is incorrect on both wheels, then this was a known fault on the Z3, and as a consequence, they produce eccentric trailing arm bushes, it is more likely that the previous owner has had these bushes changed, and put normal ones in, or has changed them and eccentric ones have been fitted.

If the beam was bent I am fairly sure it would only affect one side.

Have you spoken to the previous owners, or do you have any receipts for work done to the car in the history file?

 

[oldcarman]

Sounds to me that you're being Fluxed. Keep your car away from these people, sounds to me like they want to fleece you for big bucks for something that isn't there. I poured over my service manual and pics, etc last evening and quite simply find their scenario lacking substance. If a BMW rear carrier in any model bent that easily it would have shown up previously. Surely you've watched rally cars clearing air and landing without bending the diff even with the amount of torture they receive. HTH's JIM

 

[roadvoyager1]

That said if the toe is incorrect on both wheels, then this was a known fault on the Z3, and as a consequence, they produce eccentric trailing arm bushes, it is more likely that the previous owner has had these bushes changed, and put normal ones in, or has changed them and eccentric ones have been fitted.

Would these be the "offset bushings" mentioned in the link that Cooper posted? I agree with Zedonist; it sound more feasible an explanation, particularly if there is no damage to other suspension parts or mountings. Is there any impact damage visible on the rear axle carrier itself that would indicate a very heavy impact? I would check the mounting points very carefully as the movement in them would be small. Lets hope that it turns out to be a simple bushing issue and you can get the car back on the road easily.

 

[Dino D]

This sounds suspect to me. If was as easy to do as this mechanic says then more than half the Z 'a UK would be suffering from it.
Mine should be dead if it was so easy to do- have you seen the A and B roads in Kent?!

What is brand of tyres and how wide are they and the rims?

 

[zedonist]

Would these be the "offset bushings" mentioned in the link that Cooper posted? I agree with Zedonist; it sound more feasible an explanation, particularly if there is no damage to other suspension parts or mountings. Is there any impact damage visible on the rear axle carrier itself that would indicate a very heavy impact? I would check the mounting points very carefully as the movement in them would be small. Lets hope that it turns out to be a simple bushing issue and you can get the car back on the road easily.

Yes item 8 in the diagram, there are two part numbers in real oem.

BMW TIS online
Technical and background information on vehicles BMW and Mini
33 32 ...Correction positive rear toe (compact, Z3)
Correction positive rear toe necessitated by summing the unfavorable tolerances can be made by ekstsentirkovyh rubber-metal hinges.

Warning!
In any case should not use this method in "elimination" of changes in the axial geometry that occurred as a result of the accident.

Set the instrument to measure the wheel alignment KDS millimeter scale.
Perform wheel alignment with this scale.

Determination of the correction value, for example:

Actual value toe rear left wheel+ 2.5 mm
Setpoint toe rear left wheel+ 1.5 mm
Correction value toe1.0 mm

Determined from this chart below for the respective side (left / right), increasing or decreasing the number of toe (0 to 9) for the correction value (eg, 1 mm).
Apply by on both sides of the eccentric rubber-metal hinge (naprmer, 4.5) and connect auxiliary line.

Note:

If the adjustment with an external eccentric rubber-metal joint is insufficient, you can also install a hinge inside.

Remove the trailing arm,
refer to 33 32 000.

Lubricate the external flange rubber-metal hinge structure Circolight (see Parts Service BMW).

Pull the rubber-metal joint with special tool 33 3 051/052/053/054.

Note:
Pay attention to the installation direction of the rubber-metal hinges.

Make a mark on the trailing arm bushing podaveski side fitting, as shown in the figure.

Lubricate the eccentric rubber-metal hinge (1) composition Circolight (see Parts Service BMW) and install it on the trailing arm so that the mark on the sleeve of the trailing arm coincided with the auxiliary line.It should be remembered that made whether to increase or decrease toe, see this chart below (reference point).
Insert the rubber-metal hinge (1) with special tool 33 3 051/052/054/055.

Install the trailing arm and make control wheel alignment.

Chart correction toe-to-left wheel

1 direction of movement
2, the direction of motion, the inner rubber-metal hinge

3 direction, the outer rubber-metal hinge

4 direction Joining

5 reference point - increasing toe

6 reference point - reducing toe

7 trailing arm bush
8 rubber-metal hinge

9 increase in toe

10 decrease in toe

11 torsion angle

12 change in toe

Chart correction toe-to-right wheel

1 direction of movement
2, the direction of motion, the inner rubber-metal hinge

3 direction, the outer rubber-metal hinge

4 direction Joining

5 reference point - increasing toe

6 reference point - reducing toe

7 trailing arm bush
8 rubber-metal hinge

9 increase in toe

10 decrease in toe

11 torsion angle

12 change in toe

 

[FluxMorz]

This is probably going to be a rather unfitting response but I'll try as best I can. The suspension fellow turns out to be a friend of my uncle's and when my Dad mentioned this he waived all expenses so far (wasn't much anyway, but still). He also wasn't phased or surprised at all when we suggested taking the car home to do it ourselves. It can't have registered as a big hit to his income at least.

He explained that he had most often come across this problem on Holden Commodores (an popular Australian car) where the car has been hit in the front end while moving (dickheads hoon in these cars constantly, and are always colliding with gutters, poles, guard rails, other cars and etc), and because the car has been stopped at the front end, and the back end has still tried to move forward (think a head on collision for example), the movement has bent the rear cross member. My father (an ex-mechanic from maaaany moons ago) was there - and we were all under the hoisted car as this was being shown to us - and he agreed with the fellow, except he felt the car was more likely to have been hit in the front of the cross member itself from some sort of jutting rock, or lump of wood, or something on the road, rather than having been in a front end collision. He feels the manufactured hole (which I point out in the diagram I posted, even though it isn't drawn there) is a structural weakness which would allow for this kind of bend more easily.

I will also go on to say that I don't feel the tow is exactly the same on both sides (but I'd have to confirm this) because one did wear worse than the other, but they were still in very comparable states of wear.

Regarding what t-tony said about damage to the gearbox: Yes I was confused. When the cross member bends, it pivots at the fixed points, which moves the trailing arms and pushes the differential behind it back further as well. The differential itself is not hit though, just moved out of place a bit by the string of moving items. The only thing with any apparent damage is that the cross member itself is bent slightly.

Cooper said in an email that I should mention this too: When I first got the car we had to get under it and fix where the automatic shifter mechanism had been bashed up out of place, which caused the shifter to sit at about a 95-100 degree angle instead of the 90 degree angle its supposed to. I also don't think my steptronic/sports modes work - which may be related. Fixing the angle of the shifter by putting the mechanism back how its supposed to sit under the car was pretty easily done, though. Could be related? I suppose it could at least.

The previous owner was an egotist and whilst pleasant enough to speak to, would never give a straight answer that wasn't 100% complimentary to the car. It was a job just trying to word questions in a way that would get helpful response from him. He did provide full service history and receipts though. But, it would be easy just to forget to include receipts relating to unreported damage or changes.

I'll talk to my father and try to address some of the technical posts later I guess. I need his smarts to address that. Its all over my head.

 

[zedonist]

Just buy a second hand rear carrier and get it fitted, lowest cost option.

I offer this solution as providing further technical help that is dismissed because of opinion is a waste of effort.

I would add this though speed and rocks are the same on any continent, the hole in the structural member is welded on all sides, and so is very strong, therefore if the car has had such an impact as suggested then I for one would turn the car into a big metal cube.

Just my opinion you understand

 

[miller1098]

It's the bushes

View: http://m.youtube.com/watch?v=pU09D4MFgo8

 

[roadvoyager1]

Even if it does not resolve Fluxmorz issues, and maybe relates to a fairly uncommon problem, the article posted by Zedonist must be worth adding to the Technical knowledge base (can one of the mooderators do this?). Thanks for sharing the information.

 

[GazHyde]

Let me have a look and see what I can do to move it...

 

[vintage42]

... The problem is that the rear sub frame area is all very exposed to hitting objects sticking out of the road (large rocks embedded in dirt roads, etc) and if the front of the cross member takes a hard hit to its forward side under there, then with the force of the moving car, it is possible to bend the cross member forward... I edited the above oem graphic to hopefully explain what I mean a little more. I hope it helps.

Sorry, makes no sense to me. Nor do the notes on the diagram. You could be way off on this.

 

[FluxMorz]

I want to thank everyone for their patience and help so far - particularly Zedonist and Cooper for sourcing links and graphs and etc. Unfortunately, they don't really make much sense to me a lot of the time, but I've done bits and pieces of reading and I'm trying to learn. I can tell patience is wearing thin and perhaps you all feel like I'm ignoring your responses. I was just trying to do as good a job as I can of explaining what I'm being told and giving context to it.

I came across this little bit of paper today while going through things in my car - its a wheel alignment print off that was done a month and a half or so before I bought the car. If you can understand it like my Dad seems to then you'll notice that the rear toe and camber are both way outside the acceptable tolerances.

Looking at what you all have to say about bushings being the likely culprit (again, I don't really understand) and looking briefly on ebay, it seems like a cost effective first step, before looking into further potential damage. If I can solve the issue here, then obviously I can save money on purchasing parts I may not need.

So, what would I be looking for exactly? What kind of damage and where would it be? If I need to measure anything, how do I do it? Do I need eccentric or centric bushings? I seem to have read somewhere that special tools and a LOT of effort are required to change bushings, so is this something that I will need to book in somewhere or have a mechanical friend's garage to deal with?

I'm sorry to be such a pain.

 

[FluxMorz]

Ahuh! - I also just found this: http://zroadster.org/threads/z3-rear-crossmember-bush.4958/#post-57222